Tobacco use continues to be a major public health problem in the United States with approximately one-third of users becoming dependent and tobacco smoking is the leading avoidable cause of death in the United States. The present proposal focuses on animal studies to investigate neurobiological mechanisms that mediate nicotine addiction. An animal model of increased intravenous self-administration of nicotine to the point of dependence has been developed and will be further refined, validated and compared to acute reinforcement models. Preliminary results show that a CRF-1 antagonist can block both the anxiety-like responses associated with acute nicotine withdrawal and the increase in nicotine responding produced by nicotine deprivation in an extended access model. The overall hypothesis of the present proposal is that enhanced nicotine seeking in extended access (nicotine-dependent) animals is in part produced by an overactivity of extrahypothalamic corticotropin-releasing factor (CRF) stress systems and related stress modulatory agents in specific regions of the basal forebrain (extended amygdala). To test this hypothesis, three specific aims are proposed: 1). To validate an extended dependence model of nicotine self-administration in rats. 2). To explore the neuropharmacological mechanisms within specific neurochemical systems in the anxiety-like state of nicotine withdrawal. 3). To explore the neuropharmacological mechanisms within specific sites within the extended amygdala on nicotine self-administration in dependent rats. Animal models of intravenous self- administration, anxiety-like responses, and brain stimulation reward combined with biochemical studies, and systemic and intracerebral microinjections of specific neuropharmacological agents will be employed.
The proposed neurobiological studies will provide key information not only for the etiology of a major component of the motivation to continue to smoke once dependent, help identify those individual differences that may lead to vulnerability to dependence, and provide key targets for future medications development for the treatment of nicotine dependence.
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